Methods of fabrication of deaggregated electrically conductive polymers and precursors thereof

ABSTRACT

Deaggregated substituted and unsubstitued polyparaphenylenes, polyparaphenylevevinyles, polyanilines, polyazines, polythiophenes, poly-p-phenylene sulfides, polyfuranes, polypyrroles, polysclenophene, polyacetylenes formed from soluble precursors and combinations thereof and copolymers thereof and methods of fabrication are described. The deaggregated polymer molecules when subsequently doped show higher electrical conductivity. Agents such as lithium chloride, m-cresol and nonylphenol are used to deaggregate the polymer molecules. The deaggregating agents can be added prior to or during doping the molecules.

CROSS REFERENCE TO RELATED APPLICATION

The teaching of U.S. application Ser. No. 08/370,127, now U.S. Pat. No.5,804,100, entitled "Deaggregated Electrically Conductive Polymers andPrecursors Thereof" to M. Angelopoulos and B. Furman, filed on the sameday herewith is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention is directed to methods of fabrication ofelectrically conducting polymers having enhanced electricalconductivity. In particular, the present invention is directed tomethods to deaggregate electrically conductive polymers and precursorsthereof.

BACKGROUND OF THE INVENTION

Electrically conductive organic polymers have been of scientific andtechnological interest since the late 1970's. These relatively newmaterials exhibit the electronic and magnetic properties characteristicof metals while retaining the physical and mechanical propertiesassociated with conventional organic polymers. Herein we describeelectrically conducting polyparaphenylene vinylenes, polyparaphenylenes,polyanilines, polythiophenes, polyazines, polyfuranes, polypyrroles,polyselenophenes, poly-p-phenylene sulfides, polyacetylenes formed fromsoluble precursors, combinations thereof and blends thereof with otherpolymers and copolymers of the monomers thereof. In order for thesematerials to be used in place of metals in more applications, it isdesirable to increase the conductivity of these materials.

The article "The Concept of Secondary Doping as Applied to Polyaniline",A. G. MacDiarmid, A. J. Epstein, Synthetic Metals, 65 (1994), 103-116,describes increasing the electrical conductivity of a polyaniline byexposing a doped polyaniline to a secondary dopant, such as meta-cresol.MacDiarmid et al. teaches that the secondary dopant results in anintra-molecular conformational change in the polyaniline molecule. Priorto being exposed to the secondary dopant, the doped polyaniline moleculeis in a compact coil intra-molecular conformation. Intra-molecularconformation refers to the conformation of a single molecule or a singlepolymer chain in which the molecular chain is coiled around itself. Incontra-distinction inter-molecular structure refers to the structuralarrangement of more than one molecule or polymer chain in which themolecules or chains are bonded together or coiled around each otherforming aggregates. These aggregates are then comprised of many polymerchains intertwined or entangled. MacDiarmid et al. teaches that thesecondary dopant causes a intra-molecular conformational change, i.e.,the molecule or the chain unravels and assumes an expanded coilconformation. A film of this expanded coil polyaniline has enhancedelectrical conductivity because of an increase in the crystallinity ofthe material formed from the aggregated straightened molecules.

In the article "Transport studies of protonated emeraldine powder: Agranular polymeric metal system", F. Zuo et al., Phys. Rev. B 36, 3475(1987) it has been reported that the polyaniline which has been dopedhas electrically conductive regions or islands which are of the order of200-300 Å. The spaces between these regions are significantly lesselectrically conductive. When an electrical current flows along thepolyaniline molecules, current flows through the electrically conductiveregions and hops over the less electrically conductive region to anadjacent electrically conductive region.

It is an object of the present invention to increase the electricalconductivity of electrically conductive polymers.

It is another object of the present invention to enhance the electricalconductivity of an electrically conductive polymer by deaggregatingaggregated molecules which are precursors of the electrically conductingpolymers so that the molecules can be more uniformly doped.

It is another object of the present invention to deaggregate polymermolecules prior to being doped to the electrically conducting state.

It is another object of the present invention to lower the glasstransition temperature of the precursor to an electrically conductivepolymer and of an electrically conductive polymer by the addition ofdeaggregating agents.

It is another object of the present invention to increase the electricalconductivity of electrically conductive polymers by extending theelectrically conductive regions or islands of the electricallyconductive polymer.

It is another object of the present invention to further increase theelectrical conductivity of a deaggregated electrically conductivepolymer by stretch orientation.

It is another object of the present invention to increase the shelf-lifeof a precursor to an electrically conductive polymer and of anelectrically conductive polymer by the addition of deaggregating agents.

SUMMARY OF THE INVENTION

A broad aspect of the present invention is a method for fabricatingelectrically conducting polymers, the electrical conductivity of whichis enhanced by deaggregating the polymer either prior to being doped tothe electrically conducting state or after being doped to theelectrically conducting state.

A more specific aspect of a method of the present invention isdeaggregating the precursor polymer or electrically conducting polymereither in solution or in the solid state, such as by using complexingagents.

Another more specific aspect of a method of the present inventionincludes steps of providing a first admixture of an additive in asolvent; forming a second admixture by dissolving in the first admixtureprecursor polymers to electrically conducting polymers wherein theadditive deaggregates the precursor molecules and either adding a dopantto the second admixture to dope the precursor to the electricallyconductive polymer or forming a film of the second admixture and thendoping the film in the solid state.

Another more specific aspect of a method of the present inventionincludes providing aniline molecules which are oxidatively polymerizedin an acid solution in the presence of a deaggregating agent to resultin a deaggregated polyaniline.

Another more specific aspect of a method of the present inventionincludes the steps of providing aniline molecules which are oxidativelypolymerized in an acid solution to form an electrically conductingpolyaniline salt which is then neutralized to the base non-doped formand deaggregated upon exposure to a deaggregating agent.

Another more specific aspect of a method according to the presentinvention includes neutralizing a polyaniline salt to the base form inthe presence of a deaggregating agent.

Another broad aspect of the present invention is a method of causing adoped electrically conductive polymer in a compact coil conformation toundergo a conformational change from a compact coil to an expanded coilconformation by exposing the doped polymer to salts and surfactants.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects, features, and advantages of the present invention willbecome apparent from a consideration of the following detaileddescription of the invention when read in conjunction with the drawingFIGs., in which:

FIG. 1 is a gel permeation chromatograph (GPC) plot of polyaniline basein NMP which shows a bimodal distribution: a very high molecular weightcomponent which is aggregated polyaniline molecules and a lowermolecular weight peak.

FIG. 2 shows a GPC plot of polyaniline base in NMP and 0.5 wt % lithiumchloride which shows that the high molecular weight peak of FIG. 1 hasbeen eliminated and the molecular weight of the other peak is actuallyhigher.

FIG. 3 is a general formula for a polyaniline.

FIG. 4A is a general formula for a doped polyaniline.

FIG. 4B is a general formula for the polysemiquinone radical cation formof doped polyaniline.

FIG. 5 is a Dynamic Mechanical Thermal Analysis (DMTA) plot ofpolyaniline base film cast from 100% NMP. (First Run;˜21% NMP remainingin film; under N₂ ; 2° C./_(min))

FIG. 6 is the DMTA plot (2nd run) of the same poylaniline film as shownin FIG. 5. This film has 0% NMP remaining in the film. The Tg is 251° C.

FIG. 7 is a DMTA plot (2nd run) of polyaniline base which has been castfrom 100% NMP doped with 1N HCl and undoped with 0.1 M NH₄ OH showing aTg of 256° C. This film has˜2.8% NMP remaining in the film.

FIG. 8 is a DMTA plot (2nd run) of polyaniline cast from NMP/0.5 wt %LiCl showing a Tg of 180° C.

FIG. 9 shows inter-molecular hydrogen bonding between undopedpolyaniline molecules.

FIG. 10 shows disruption of the intermolecular hydrogen bonding by aLiCl salt.

FIG. 11 shows a schematic view of polyaniline molecules aggregatedthrough inter-molecular hydrogen bonding.

FIG. 12 shows a UV/VIS/near IR spectrum of polyaniline doped with anorganic sulfonic acid in NMP showing a localized polaron peak.

FIG. 13 shows the same plot as FIG. 12 but with 0.5 wt % LiCl added tothe initial NMP solution from which the doped polyaniline was cast andshows a delocalization of the polaron peak.

FIG. 14 shows the same plot as in FIG. 12, but with 1 wt % LiCl added tothe initial NMP solution from which the doped polyaniline was cast andshows a significantly delocalized polaron peak.

FIG. 15 is an atomic force micrograph of a polyaniline film cast from100% NMP showing clusters or bundles of polyaniline molecules of about100 nm in size which are interpreted as aggregated regions.

FIG. 16 is an atomic force micrograph of polyaniline film cast from NMPand subsequently exposed to m-cresol.

FIG. 17 is an atomic force micrograph of the same material shown in FIG.16 with the m-cresol pumped out.

FIG. 18 is an atomic force micrograph of a polyaniline film cast fromNMP and treated with 0.5 wt % nonylphenol showing deaggregation.

FIG. 19 is an atomic force micrograph of a polyaniline film cast fronNMP and treated with 0.5 wt % triton showing deaggregation.

FIG. 20 is an atomic force micrograph of a polyaniline film cast fromNMP and treted with 1.0 wt % nonylphenol showing more deaggregation thanshown in FIG. 19.

FIG. 21 schematically shows stretch orientation of a film to enhanceelectrical conductivity.

DETAILED DESCRIPTION

The present invention is directed to enhancing the electricalconductivity of polymer materials, which when doped, are electricallyconducting. Examples of polymers which can be used to practice thepresent invention are of substituted and unsubstitutedpolyparaphenylenes, polyparaphenylevevinylenes, polyanilines,polyazines, polythiophenes, poly-p-phenylene sulfides, polyfuranes,polypyrroles, polyselenophenes, polyacetylenes formed from solubleprecursors and combinations thereof and copolymers of monomers thereof.The general formula for these polymers can be found in U.S. Pat. No.5,198,153 to Angelopoulos et al. The present invention will be describedwith reference to one type of polymer which is a substituted orunsubstituted polyaniline or copolymers of polyaniline having generalformula shown in FIG. 3 wherein each R can be H or any organic orinorganic radical; each R can be the same or different; wherein each R¹can be H or any organic or inorganic radical, each R¹ can be the same ordifferent; x≧1; preferably x≧2 and y has a value from 0 to 1. Examplesof organic radicals are alkyl or aryl radicals. Examples of inorganicradicals are Si and Ge. This list is exemplary only and not limiting.The most preferred embodiment is emeraldine base form of the polyanilinewherein y has a value of approximately 0.5.

In FIG. 4A polyaniline is shown doped with a dopant. If the polyanilinebase is exposed to cationic species QA, the nitrogen atoms of the iminepart of the polymer becomes substituted with the Q+ cation to form anemeraldine salt as shown in FIG. 4A Q+ can be selected from H+ andorganic or inorganic cations, for example, an alkyl group or a metal.

QA can be a protic acid where Q is hydrogen. When a protic acid HA isused to dope the polyaniline, the nitrogen atoms of the imine part ofthe polyaniline are protonated. The emeraldine base form is greatlystabilized by resonance effects. The charges distribute through thenitrogen atoms and aromatic rings making the imine and amine nitrogensindistinguishable. The actual structure of the doped form is adelocalized polysemiquinone radical cation as shown in FIG. 4B.

The emeraldine base form of polyaniline is soluble in various organicsolvents and in various aqueous acid solutions. Examples of organicsolvents are dimethylsulfoxide (DMSO), dimethylformamide (DMF) andN-methylpyrrolidinone (NMP). This list is exemplary only and notlimiting. Examples of aqueous acid solutions is 80% acetic acid and60-88% formic acid. This list is exemplary only and not limiting.

Although the present invention is described in terms of polyaniline, itis not limited thereto.

FIG. 1 shows a GPC (gel permeation chromatograph) of polyaniline in thebase form dissolved in 100% solvent N-methylpyrrolidinone (NMP). Thevertical axis is the ultraviolet visible (UV VIS) detector response andthe horizontal axis is the peak retention time in minutes. Two peaks areevident in FIG. 1, peak 2 which corresponds to a weight averagemolecular weight of approximately 371,700 and peak 4 which correspondsto a weight average molecular weight of approximately 29,500.

FIG. 2 shows the GPC of polyaniline in the base form in NMP/0.5 wt %lithium chloride (LiCl) which shows a single peak 6 corresponding to aweight average molecular weight of approximately 45,500. It is evidentin comparing FIG. 1 to FIG. 2 that the high molecular weight peak 2 ofFIG. 1 has disappeared and that the molecular weight of the major peakis higher than that in NMP, corresponding to a higher hydrodynamicvolume.

FIG. 5 is a plot of a first run of a dynamic mechanical thermal analysis(DMTA) plot of an undoped polyaniline base film cast from 100% NMP. Theas-cast film contains approximately 21% NMP which is determined fromthermo gravimmetric analysis. The dashed line in FIG. 5 which is theplot of tan(δ) shows several transitions of which some are related tothe residual solvent.

FIG. 6 shows a plot of a DMTA (second run) of the same material as forFIG. 5. The solvent is substantially driven off in the first run. Thesingle peak of the dashed curve which corresponds to the tan (δ)measurement shows that the polyaniline base has a glass transitiontemperature (T_(g)) of 251° C.

FIG. 7 shows a plot of a DMTA (second run) for polyaniline base, castfrom 100 wt % NMP, which has been doped in 1N HCl and subsequentlyundoped with 1M NH₄ OH. Most of the NMP was removed in the process. Ithas been determined from thermogravimmetric analysis (TGA) that there isonly 2.8% NMP remaining in the film.

The glass transition temperature of this sample is 256° C., relativelythe same as that measured for the sample of FIG. 6.

FIG. 8 shows a plot of a DMTA (second run) of polyaniline base cast from99.5 wt % NMP/0.5 wt % lithium chloride. The peak in the tan(δ) curvegives a T_(g) of 180° C.

Table I summarizes the results of FIGS. 5-8 and also gives additionalresults for films cast from combinations of NMP and m-cresol and asurfactant nonylphenol.

                  TABLE I                                                         ______________________________________                                                                         Tg                                                                            from                                                                          DMTA                                         Material                                         (° C.)                ______________________________________                                        Polyaniline Base                                                                             Thermally annealed*                                                                             251                                          Cast from 100% NMP                                                                                               (0% residual NMP in film)                  Polyaniline Base                                                                                                           256HCL                           cast from 100% NMP                                                                                               undoped in ammonia                                                                              (2.8% residual NMP                      in film)                                                       Polyaniline Base                                                                                                     186ally annealed*                      cast from 90 wt %                                                             NMP/10 wt % m-cresol                                                          Polyaniline Base                                                                                                     175ally annealed*                      cast from 75 wt %                                                             NMP/25 wt % m-cresol                                                          Polyaniline Base                                                                                                     180ally annealed*                      cast from 99.5 wt % NMP/                                                      0.5 wt % LiCL                                                                 Polyaniline Base                                                                                                     222ally annealed*                      cast from 99 wt %                                                             NMP/1 wt % nonylphenol                                                        ______________________________________                                         *Thermally annealed  scanned to 350° C. under N.sub.2 at 2°     C./min                                                                   

The drop in glass transition temperature of the polyaniline base uponexposure to an additive such as m-cresol, LiCl and nonylphenol indicatesthat there is a drop in the crosslink density of the polyaniline basematerial as a result of deaggregation of the polyaniline base molecules.While applicant's do not want to be limited to a particular theory, thiscross-link is believed to be in the form of inter-chain orintermolecular hydrogen bonding.

FIG. 9 shows two polyaniline base molecules wherein a hydrogen atom froman amine site on one molecule is hydrogen bonded as represented by thedashed line to an imine nitrogen on an adjacent molecule.

FIG. 10 shows the effect of adding lithium chloride to the arrangementshown in FIG. 9. The lithium chloride can complex with the iminenitrogen lone pairs as shown in the FIG. 10 thereby disrupting theinterchain hydrogen bonding between polyaniline chains.

FIG. 11 is a schematic diagram showing three polyaniline molecules 20,22 and 24 wherein there are a plurality of hydrogen bonds 26interlocking each of the three polyaniline molecules shown. It isevident from FIG. 11 that where there is a high density of hydrogenbonding between adjacent polyaniline molecules, there is effectivecrosslinking between the molecules which will affect the glasstransition temperature of a polyaniline material. (Generally the glasstransition temperature increases as the cross-linking densityincreases.) The high degree of crosslink density will result in asignificant degree of aggregation of polyaniline molecules. The atomicforce micrograph (AFM)(FIG. 15) of the polyaniline film processed from100% NMP shows "clusters" or "bundles" on the order of 100 nm. Thisstructure agrees well with previous results on evaporated films (nosolvent) by T. L. Porter ct al., Surface Science, 293, 81 (1993). Whenthe hydrogen bonded and ravelled molecules of FIG. 11 are exposed to adeaggregating agent such as LiCl, an inter-molecular structural changeoccurs wherein the molecules are no longer hydrogen bonded and themolecules are unravelled and deaggregated.

The present results together with the previous results by Porterindicate that polyaniline in the solid-state is highly aggregated.(Examples of solid state forms of polymers are powders and films.) Whenthe polyaniline is then dissolved in NMP, the NMP does not appreciablysolvate the polyaniline to disrupt the interchain interactions of thepolyaniline and the material remains aggregated. When the polyanilinemolecules are exposed to a dopant, this high degree of aggregation willprevent the dopant from being able to dope all regions of thepolyaniline molecules uniformly and may be responsible for the formationof the metallic islands characteristic of conducting polyaniline(described above) which are approximately 200-300° A. This will resultin less than an optimal conductivity for a doped polyaniline material.If the aggregated polyaniline molecules are deaggregated by the methodsaccording to the present invention, the polyaniline molecules will bemore effectively doped when contacted with a dopant. In this fashion thesize of the metallic islands may in turn be increased above 200-300° Athereby enhancing the mobility of the carriers, and in turn theelectrical conductivity. It may be possible to ultimately eliminate theformation of islands by more uniform doping; in this fashion thematerial would be more homogeneous and hopping through less conductingregions to go from metallic island to metallic island would thereby beeliminated.

An exemplary list of solvents useful to practice the present inventionis:

List of Solvents

N-methyl pyrrolidinone (NMP)

dimethyl sulfoxide (DMSO)

dimethyl formamide (DMF)

pyridine

toluene

xylene

m-cresol

phenol

dimethylacetamide

tetramethylurea

n-cyclohexylpyrrolidinone

aqueous acetic acid

aqueous formic acid

pyrrolidinone

N,N' dimethyl propylene urea (DMPU)

benzyl alcohol

water

An exemplary list of salts which can be used as a deaggregation agent oradditive is:

Salts

lithium chloride

lithium bromide

lithium iodide

lithium fluoride

lithium tetrafluoroborate

lithium hexafluorophosphate

lithium perchlorate

lithium phenoxide

lithium triflate

lithium niobate

magnesium bromide

magnesium chloride

magnesium ethoxide

magnesium fluoride

magnesium sulfate

magnesium perchlorate

magnesium nitrate

sodium bromide

sodium chloride

sodium chlorate

sodium hexafluorophosphate

potassium bromide

potassium chlorate

potassium chloride

potassium fluoride

potassium hexafluorophosphate

rubidium chloride

rubidium fluoride

rubidium nitrate

cesium bromide

cesium chloride

cesium floride

cesium iodide

calcium bromide

calcium chloride

calcium iodide

calcium nitrate

barium chloride

barium fluoride

barium iodide

barium sulfate

barium perchlorate

tetrabutylammonium chloride

tetrabutylammonium fluoride

tetrabutylammonium hexafluorophosphate

tetrabutylammonium iodide

tetrabutylammonium nitrate

tetraethylammonium iodide, etc.

tetramethylammonium bromide, etc.

tetrapentylammonium bromide, etc.

An exemplary list of surfactants which can be used as a deaggregationagent or additive is:

Surfactants

Reference: Encyclopedia of Chemical Technology, 3rd Edition, K. Othmer,Wiley-Interscience, Pub., vol. 22, p. 332

Cationic, anionic, nonionic, and amphoteric surfactants included.

Examples of each are given below:

(I) anionic surfactants--Examples

i) Carboxylates RCOOM R is hydrocarbon chain,

M is a metal or ammonium ion

e.g., 3M Fluorad series, polyalkoxycarboxylates

ii) sulfonates RSO₃ M R is alkyl, aryl, or

alkylaryl groups, M is a metal or ammonium ion

e.g., alkylbenzene sulfonates such as dodecylbenzene

sulfonate sodium salt, nonylbenzene sulfonate sodium salt,nonylnaphthalene sulfonate sodium salt

alkylarenesulfonates, lignosulfonates,

naphthalenesulfonates,

alpha-olefinsulfonates, sulfonates with ether,

amide, or ether linkages, such as dialkyl sulfosuccinates etc.

iii) sulfates R--OSO₃ M

alkyl sulfates such as octylsulfate sodium salt, 2-ethylhexyl sodiumsalt, dodecylsulfate sodium salt, dodecylsulfate lithium salt, laurylsulfate potassium salt,

alcohol sulfates, ethoxylated alcohol sulfates,

sulfated alkylphenol ethoxylates

iv) phosphates

e.g., phosphate esters such as potassium butylphosphate, potassiumhexylphosphate, phenol ethoxylated and phosphated, nonylphenolethoxylated and phosphated, dodecylphenol ethoxylated and phosphated,etc.

(2) nonionic surfactants--Examples

i) polyoxyethylene surfactants (ethoxylates)

alcohol ethoxylates R[OCH₂ CH₂ ]_(n) OH

alkylphenol ethoxylates RC₆ H₄ (OC₂ H₄)_(n) OH

e.g., Triton N-57

Triton N-111

Triton X-45

Triton X- 102

Triton X-305

Triton X-705

ii) alkylphenols, e.g. nonylphenol, docecylphenol

iii) glycerol esters of fatty acids

iv) polyoxyethylene esters

v) carboxylic amides

vi) polyoxyethylene fatty acid amides

vii) polyalkylene oxide block copolymers

viii) poly(oxyethylene-co-oxypropylene)

e.g., pluronic series

(3) cationic surfactants

aliphatic mono, di, and polyamines derived from fatty and rosin acids

alkylamine ethoxylates

amine oxides

alkoxylates of ethylenediamine

2-alkyl-1-(2-hydroxyethyl)-2-imidazolines

quaternary ammonium salts

e.g. dialkyldimethylammonium salts

alkylbenzyldimethylammonium chlorides

alkylpyridinium halides

(4) amphoteric surfactants

Examples: imidazolinium derivatives

alkylbetaines

amidopropylbetaines, etc.

An exemplary list of acidic additives which can be used as adeaggregation agent or additive is:

Acidic Additives

(1) Preferred acidic additives

naphthol

thiocresol

2-hyoxydibenzofuran

1-[2-(2-hydroxyethoxy) ethyl] piperazine

2-hydroxy-9-fluorenone

5-hydroxyisoquinoline

2-hydroxy-1,4 naphthoquinone

1 -hydroxypyrene

9-hydroxyxanthene

indophenol

dihydroxynaphthalene

4-propyl resorcinol

2-isopropylhydroquinone

2,6 - bis(hydroxymethyl)-p-cresol

resorcinol

catechol

hydroquinone

pyrogallol

benzylalcohol

hydroxybenzylalcohol

trihydroxytoluene

iminodiphenol

(2) Acidic additives also include:

m-cresol

phenol

4-propoxyphenol

An exemplary list of dopants which can be used to dope the polymer tothe conducting state are: hydrochloric acid, acetic acid, formic acid,oxalic acid, toluenesulfonic acid, dodecylbenzene sulfonic acid,benzenesulfonic acid, naphthalene sulfonic acid, methyliodide andcamphor sulfonic acid.

When deaggregation is done in solution the deaggregating agent ispresent in an amount less than about 25 wt %. When deaggregation is donein solution using a salt as the deaggregation agent, the salt ispreferably present in an amount from about 0.00001 wt % to about 5 wt %,more preferably from about 0.0001 wt % to about 2.5 wt %; mostpreferably from about 0.001 wt % to about 1 wt %. When the deaggregationis done in solution using a surfactant as the deaggregation agent, thesurfactant is preferably present in an amount from about 0.0001 wt % toabout 10 wt %; more preferably from about 0.001 wt % to about 5 wt %;most preferably from about 0.01 wt % to about 2.5 wt %. When thedeaggregation is done in solution using an acidic additive as thedeaggregation agent, the acidic additive is preferably present in anamount from about 0.0001 wt % to about 25 wt %; preferably from about0.001 wt % to about 15 wt %; most preferably from about 0.01 wt % toabout 10 wt %.

FIG. 15, 16, 17, 18, 19 and 20 are atomic force micrographs each havinga dimension of 1000 nm×1000 nm. FIG. 15 is for polyaniline base castfrom 100% NMP; FIG. 16 is for polyaniline cast from 100% NMP andsubsequently exposed to m-cresol; and FIG. 17 of the same sample as inFIG. 16 with the m-cresol pumped out and shows no tendency tore-aggregate. FIG. 15 shows aggregated regions of the order of 100 nm.FIG. 16 shows the substantial elimination of the aggregated regionscaused by exposure to the deaggregating agent, m-cresol, which remainswhen the m-cresol is removed. Therefore, the deaggregated structure islocked or remains without the deaggregating agent. FIG. 15 shows bundlesof aggregated regions which are not present in FIG. 16 and 17. FIGS. 18,19 and 20 show similar results for treatment with nonylphenol and tritonsurfactant. The level of deaggregation is not as complete as in FIG. 16but shows the onset of deaggregation.

Basic Synthesis of Polyaniline

Unsubstituted Polyaniline

The unsubstituted polyaniline is synthesized by the chemical oxidativepolymerization of aniline in 1N HCL using ammonium peroxydisulfate as anoxidizer. Polyaniline can also be oxidatively polymerizedelectrochemically as taught by W. Huang, B. Humphrey, and A. G.Macdiarmid, J. Chem. Soc., Faraday Trans. 1, 82, 2385, 1986. In thechemical synthesis, the conducting polyaniline:hydrochloride saltprecipitates from solution. The polymerization is allowed to proceed forseveral hours after which the powder is filtered, washed with excess 1Nhydrochloric acid. The polyaniline:hydrochloride is then converted tothe non-conducting or non-doped polyaniline base by reaction with 0.1Mammonium hydroxide. The polyaniline base is then filtered, washed withammonium hydroxide, then washed with methanol and dried. The polymer inthis stage is in the undoped base form as a powder.

The polymer is generally processed by taking the polyaniline base powderand dissolving it in organic solvents, most commonlyN-methylpyrrolidinone. This solution can be used to spin-coat thin filmsof the base polymer or can be used to solution cast thick films or canbe used to fabricate structural parts of the polyaniline base. Thesubstituted polyaniline derivatives are made by the oxidativepolymerization of the appropriate substituted aniline monomer.Copolymers can also be made by the oxidative polymerization of one ormore monomers. In addition different acids other than hydrochloric acidcan be used in the synthesis.

Doping generally involves reaction with most commonly protonic acids.Other electrophiles can also be used as dopants, for example alkylatingagents, etc. The doping can be done in solution or it can be doneheterogeneously in the solid state. For example, the NMP solution of thepolyaniline base can be used to spin-coat films of the polyaniline base.These films can be doped or made conducting by dipping into a solutionof the appropriate acid such as 1N HCL, or aqueous toluene sulfonic acidor the vapor of the acid. The polyaniline base powder can also be dopedby stirring in an aqueous solution of the dopant. The doping can also becarried out in solution which is generally preferred as it allows theconducting form to be processable. To the NMP solution of thepolyaniline base is added the appropriate dopant, for examplecamphorsulfonic acid. The acid reacts with the polyaniline base to formthe conducting polyaniline salt. Any other acid or electrophile can beused in the same manner. The conducting salt will either precipitate orremain in solution depending on the particular dopant used. If it staysin solution, the conducting solution can then be used to fabricate filmsof the conducting polyaniline by spin-coating, (lip coating,spray-coating, etc. or fabricated into some structural components.

Typical experimental for the additives: The present invention usesadditives in the starting solvent, eg. NMP. For example, 0.00001 wt % to5 wt %, preferably 0.0001 to 2.5%, and most preferably 0.001 to 1% ratioLiCl is added to the NMP. The salt is allowed to dissolve in the NMP. Tothis solvent is added the polyaniline base powder and allowed to stir.Once the polyaniline base is dissolved, it is filtered through a 0.2micron millipore filter and then to the filtered solution is added thedopant. Dopants used in this study include toluenesulfonic acid, camphorsulfonic acid, acrylamidopropanesulfonic acid, hydrochloric acid.

The conductivity of the polyaniline salt is found to depend on theprocessing conditions. Generally polyaniline doped heterogeneously withaqueous 1N HCL gives conductivity on the order of approx. 1 S/cm. Dopingin NMP generally gives much lower conductivity (approx. 0.1 S/cm). Agreat deal of variation in conductivity has been observed depending onthe solvent system used for doping. When a polyaniline base is doped inNMP with an organic sulfonic acid a localized polaron peak is observedon the ultraviolet-visible near IR spectrum. When this film is exposedto m-cresol a highly delocalized polaron peak is observed extending outto 2500 nm with the conductivity increasing to hundreds of S/cm.Conductivity of 0.2 S/cm is attained when an NMP solution of thepolyaniline base is reacted with camphorsulfonic acid oracrylamidopropanesulfonic acid. The uv/visible/near IR spectrum for thepolyaniline doped with acrylamidopropane sufonic acid is shown in FIG.12. As can be seen a localized polaron peak 10 is attained. When 0.5 wt.% LiCl is added to the NMP, a delocalized polaron peak 12 (FIG. 13) isattained and with 1 wt. % LiCl a highly delocalized polaron peak isattained (FIG. 14). This delocalized polaron is indicative of higherconductivity as a result of more highly delocalized carriers.

Also, an NNP/additive (e.g. LiCl) solvent system was used to spin-coatthe polyaniline base films. The UV of the base also shows a red shift tolonger wavelengths with the incorporation of additives as compared tofilms cast from 100% NMP. This red shift is indicative of an extensionof the conjugation length. When these films are doped with hydrochloricacid vapor, the films which include the lithium chloride show a morehighly delocalized polaron peak as compared to the NMP film alone.

The additives can also be surfactants such as nonylphenol or thetritons. The triton for example is dissolved in the NMP prior to theaddition of the pani base as described above. This solution was used tocast thick films of the pani base. Upon doping of the thick films withhydrochloric acid, the conductivity of the film was 11 S/cm for thetriton containing film; 40 S/cm for the nonylphelnol containing film;and only 1 S/cm for the NMP only film.

Films processed according to the present invention can give rise toenhanced stretch orientation and a corresponding increase in electricalconductivity.

FIG. 21 schematically shows an undoped deaggregated film 20 held at end22 and end 24 by clamps 26 and 28 respectively. Ends 22 and 24 arepulled apart as indicated by arrows 30 and 32, respectively. Themolecules in the deaggregated film are unravelled and therefore whenfilm 20 is stretched there is increased propensity for alignment of themolecules in the stretch direction and thereby enhanced electricalconductivity in the stretch direction.

Solutions processed according to the present invention exhibit enhancedshelf life stability. Polyaniline solutions in general tend to gel overtime. The time for gelling to occur is dependent on solvent andconcentration of solids in solution. For example, a solution ofpolyaniline base in NMP made to 5% solids by weight tends to gel withindays. Solutions higher in solids content gel within minutes. Gellationlimits the full use of the polyaniline solutions for many applications.Gellation occurs because of interactions between chains, most probablyhydrogen bonding. As the hydrogen bonding between chains increase, chainentanglements increase. As this entangled or highly aggregated structureis less soluble than the non-aggregated structure, the solutions of theaggregated structure in turn gel. The addition of salts such as lithiumchloride, for example, breaks the interchain hydrogen bonds and in turnprevents the solution from gelling thereby enhancing the long term shelflife stability of the polyaniline solutions. Also, the use of theseadditives allows higher solids polyaniline solutions to be made (higherthan can normally be made without the additives) with good shelf lifestability.

While the present invention has been described with respect to preferredembodiments, numerous modifications, changes, and improvements willoccur to those skilled in the art without departing from the spirit andscope of the invention.

What is claimed is:
 1. A method comprising the steps of:providing afirst admixture of an additive and a solvent; forming a second admixtureby dissolving in said fist admixture precursor polymers to electricallyconducting polymers, said additive deaggregates said precursormolecules; thereafter adding a dopant to said second admixture to dopesaid precursor to be an electrically conductive polymer; said precursoris a polyaniline, said additive is lithium chloride and said solvent isselected from the group consisting of N-methylpyrrolidinone andm-cresol.